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The First Steps
Toward Understanding the Nature of
Footwear Impression Evidence

SINCE THE VERY BEGINNING, criminals have left their footmarks at the scene of the crime. It is an undeniable law of gravity that even the most intelligent criminal mind cannot circumvent. Criminals may easily don latex gloves but nary a one will commit their crimes wearing shoe covers. These impressions are an unclaimed bounty waiting to be discovered, and all that stands in our way is the proper tools and the knowledge of their application.

Footwear impressions represent the ultimate enigma in forensic science. They are among the most prevalent types of evidence to be

Figure 1—This is an example of a "dry impression" which is often a reproduction of a shoe's outsole in a dry medium such as dust or dirt.

Figure 2—A "wet-origin impression" can be a reproduction of the shoe's outsole in a wet medium such as snow, water, or oil.

found at crime scenes, but they are simultaneously the least sought-after clues. Over the years, a number of myths regarding footwear evidence have permeated our lexicon and drained our institutional knowledge of effective processing techniques. Police officers and criminalists alike are disadvantaged by this condition, resulting in valuable evidence going unnoticed.

Fortunately, there is a simple solution and the learning curve is slight. By understanding the nature of footwear impressions, we can better understand the best practices for recovering them.

Footwear impressions can tell us about both the criminal and the crime. We may be able to determine the make and style of shoe, and even the identity of the shoe to the exclusion of all others in the world. We can even use these impressions to rule out certain shoes and narrow the suspect pool.

Equally important is our ability to use footwear to tell us how the criminals moved through the scene. Did they climb through a window or boot open a locked door? Did they walk away from the scene or run? Did they enter a particular room or leave it untouched? All of these questions may be answered—but only if we discover the impressions.

European police agencies have made great strides in developing and collecting footwear impressions. Many agencies are reporting footwear evidence being collected in over 70 percent of their cases. This is quite remarkable compared to most agencies in the United States. It isn’t that the Europeans are smarter or more sophisticated; they are simply more dedicated to finding this type of evidence. When I began training officers years ago, I took surveys that showed they rarely recovered any footwear evidence. After training officers in the proper techniques, I found that number to rise significantly. As for myself, I have been able to recover footwear evidence in approximately 80 percent of my cases.

It has been my experience that meaningful training in the recovery of impression evidence is rare, and in some cases the instruction is wrong. In reality, there are few practitioners and even fewer experts. Many investigators simply do not know how to properly collect this valuable evidence. Often, recovery techniques are the result of haphazard or improvised methods to the situation. These methods are often passed down from one practitioner to the next, or lost forever due to retirement or termination. Additionally, many agencies do not provide the proper equipment, which in many cases is very affordable. All of these circumstances lead inevitably to handicaps that are difficult to reverse.

The first step to improving the quality of these collection techniques is to better understand the impression and how various techniques affect its overall condition. Use the wrong technique and you can ruin the impression. Use the right technique… Well, you just might make the case.

The second component to improving collections is a little bit tougher to accomplish. It requires us to improve our awareness of footwear evidence—and then search it out.

Impressions are generally categorized first as either two dimensional (those having a length and width but no depth) and three dimensional (having width, length, and depth). Three-dimensional impressions are always visible, while two-dimensional impressions may be “latent,” or invisible to the naked eye. Think of these impressions in the same way you think of latent fingerprints. Two-dimensional impressions can be further sub-categorized.

There are basically two kinds of latent two-dimensional footwear impressions. Dry impressions are reproductions of the shoe’s outsole in a dry medium such as dust or dirt (Figure 1). These impressions are fragile and can be easily damaged. That is because the “dust” is resting on the surface with a very weak bond, just like dust on your furniture. Any force or pressure applied by another object may result in irreversible damage to the impression. Positive impressions are the most common, but negative or reversed impressions are sometimes encountered as well. In either case the collection techniques are the same.

The second type of latent mark is described as a wet-origin impression (Figure 2). These impressions are defined as a reproduction of the outsole in a wet medium such as snow, water, or oil. Once dried, these impressions may be indistinguishable to the average officer from dry-origin impressions. These marks are typically more durable than dry-origin, but they can be damaged with improper handling.

Both types of impressions can be found on a variety of surfaces at the crime scene, including linoleum, glass, toilets, counters, or even paper. Of course, the first method of documentation is always photography, which would be an article in and of itself. This article will only discuss lifting methods of recovery and not casting or photography techniques.

The easiest way to search for these impressions is by using strong oblique lighting. This is most commonly accomplished by shining a strong flashlight at a low angle relative to the surface containing the impression (see photo on the Page 10). You can further enhance this technique by turning off any room lights or by shading the area with a dark material like a jacket or blanket.

Once a suspect footwear impression is located and photographed, you can turn your attention to lifting techniques. This is where the fun starts. As stated earlier, the officer may not be able to readily distinguish dry-origin impressions from wet-origin impressions. As a result, techniques that may have worked before may not work well now. I once had a criminalist state to me that they had used black fingerprint powder to develop a clearly visible print. When they applied the powder, the impression simply disappeared. I asked them if it was a dry-origin impression and I received only a blank stare. Herein lies the problem.

Distinguishing between the two types of prints can be difficult. In some cases it will be readily apparent. In others, it may be nearly impossible for the inexperienced investigator to distinguish. Even the most experienced examiners may not be able to distinguish a dry-origin impression from a wet-origin one. Oftentimes, the environmental conditions may aid the investigator in making a rational decision.

For example, if the suspect had to walk through snow or rain to get to the point of entry, then you are probably going to be dealing with wet-origin impressions at that position. If, on the other hand, the weather has been arid and dry, then you may be dealing with dry-origin impressions. This seems like a simple realization, but the connection is easily lost on some—especially when your attention is spread over various aspects of the scene like security, interviews, general processing, and searching.

As the practitioner gains additional experience, they may feel more comfortable in determining the impression type by sight and scene conditions. Until that time comes, there is a simple methodology to follow that offers the safest, most effective means of collecting both types of impressions. As in medicine, crime-scene investigators strive to “do no harm” and preserve evidence in a condition as close to the original as possible. Following this model, we work from the least destructive methods to the most destructive ones.

My advice is to begin by treating all impressions as dry-origin impressions. I say this because most of the techniques used for collecting dry-origin marks are less destructive than those for wet-origin marks. After photography with oblique lighting, I would recommend the use of an electrostatic dust print lifter (ESDL). There are several models available from vendors and a good handheld unit can be found for as little as $600.

The ESDL technique involves the use of a metalized film that is placed over the impression. A grounding plate or film strip is placed adjacent to the lifting film and the electric nodes on the lifting device are bridged between the two. Some units have embedded nodes while other models utilize wires with alligator clips or similar conductive ends. A static charge is then sent through the film and—in theory, anyway—the dust from the impression is attracted to the film where it settles. It can then be transported back to a darkroom for further photography.

ESDLs are nice because they usually allow for several lifts of the impression and they can be used on a variety of surfaces including doors, glass, counters, paper, fabrics, carpet, and even human skin. The handheld units are very convenient to carry and the time to gain proficiency can be measured in hours. They are also very safe to use provided the practitioner follows some simple safety guidelines outlined by the manufacturers.

One important word of caution: In order to see the impression on the lifting film, you will likely need to view the film in a darkened room with strong oblique light. I have often used a bathroom or utility room in the crime scene for such inspections. If you properly use the device and you do not see the impression on the lifting film but you do see the impression remaining on the surface, then you can proceed to wet-origin lifting techniques.

If you conclude that the impression is of wet origin, you have two good options. One is the use of a gel lifter. The other option is the application of fingerprint powder followed by lifting with a gel lifter or fingerprint tape. In some cases, you may be able to lift the impression directly with a dark-colored (black) gel lifter. These lifting sheets are typically 6 x 14 inches and come in black or white.

If multiple impressions exist, you may want to experiment with a small portion of one print before applying powder to all prints present. The selection of powder color is not very significant, but I would suggest black or silk black to provide the best contrast. The powder is applied as you would to a fingerprint. Once the print is developed, it can be lifted with a contrasting-colored gel lifter or fingerprint tape.

Understanding the nature of these two impression types is your best defense against inadvertently damaging evidence through the application of an improper technique. These are simple mistakes with potentially devastating results. With a little practice and a little patience you can learn to maximize your efforts in collecting this valuable evidence.

About the Author

Tom Adair is a board-certified footwear examiner with the IAI (International Association for Identification). He is a past member of SWGTREAD; he co-founded the Colorado Forensic Foot-wear Information Network (COFFIN); and he is a past president of the Association for Crime Scene Reconstruction. Adair has authored more than 50 papers in forensic journals.

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